Electrical device



Sept. 12, 1939. A. G. ANDEEN ELECTRICAL DEVICE Filed Sept. 11, 1936 42 /5' l3 //VV[N70/? Aa A/vanw Br A44 Mm ATTORNEY Patented Sept. 12, 1939 UNITED STATES PATENT OFFICE ELECTRICAL DEVICE Application September 11, 1936, Serial No. 100,299

4 Claims.

pression plates with screws or bolts extending.

through openings in the pile-up, the contact springs being insulated from the bolts by bushings of rigid insulating material, usually hard 13 rubber. In practice the bushings, on account of their frangible character, have been predeterminedly made nominally shorter than the length of the openings to prevent breaking of the bushings during compression of the pile-up, but due m either to an extra long bushing, or to an extra short bushing, the bushings occasionally catch against an edge of one or the other of the springs, strips or plates and breakages occur. Furthermore, breakages occur due to slight variations in the over-all dimension of the pile-up within tolerable limits. Also because of interstices usually present in the pile-up loose metal particles therein at times cause short circuits during assembly of the telephone system at the ex- 30 change, due to the fact that the loose metal particle changed its position after inspection had been completed by the manufacturer of the contact spring pile-ups.

Objects of the present invention are-to improve the construction and simplify the assembly of such contact assemblies whereby the difliculties above mentioned are overcome.

In accordance with the above objects, the invention as applied to an electrical contact spring 40 assembly or pile-up, such as is used extensively in circuit controlling apparatus or as commonly called sequence switches, embodied in automatic telephone exchanges, of the class shown in U. S. Patent 1,127,808 to J. N. Reynolds et al., Feb- 45 ruary 9, 19 5, contemplates an assembly comprising alternating springs and insulator strips .and external compression plates with retaining screws passing through openings in the pile-up. Surrounding the screws are bushings of rubber o which'are sufiiciently soft during assembly to cold flow laterally when compressed longitudinally so that breakage will not occur and of a length slightly greater than the final distance between the compression plates so that the ex- 55 cess rubber will ioroe any loose particles of metal permanently into position either where they will produce no short circuit or will produce a short circuit which will be detected during inspection.

Other objects and advantages of this invention will more fully appear from the following de- 5 scription taken in connection with the accompanying drawing, wherein V Fig. 1 is a fragmentary side elevational view, partly in section, of a sequence switch used in automatic telephone exchanges capable of employing an electrical contact spring assembly of this invention;

Fig. 2 is a sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is a detail sectional view on an enlarged scale taken on the line 3-3 of Fig. 2 showing the improved construction of contact spring assemb y;

Fig. 4 is an elevational view of the semi-hard rubber bushing which surrounds the retaining 2o screw of the spring assembly, the bushing being shown as it appears before being compressed longitudlnally with its length slightly greater than its final length after compression, and

Fig. 5 is a fragmentary view, similar to Fig. 3, showing the relation of the semi-hard rubber bushing to the contact springs and insulator strips before it is compressed.

Referring now to the drawing and particularly to Figs. 1 and 2 wherein there is fragmentarily shown a sequence switch of the general type disclosed in the aforementioned Reynolds et al.

patent, the numeral l0 indicates a rotatable shaft having fixed thereto in spaced relation a plurality of disks II of fiber or other insulating material. On each side of each of these ins lating disks is secured by rivets a plate of con .icting material I2, the conducting plates in the arrangement shown being electrically united. The conducting plates I2 are formed with segmental projec- 40 tions and arcuate cutout portions, whereby movable spaced contacts are provided as shown clearly in Fig. 2. Cooperating with each conducting plate H on each insulating disk H is apair of contact springs or brushes IS the pairs of contact springs l3 being arranged in assemblies or pile-ups I4, each assembly comprising four pairs of springs, secured to a U-shaped bracket IS. The springs iii are provided with terminal portions I6. Extending angularly from parallel side arms of the bracket i5 is an arm I! which is used to secure the assembly I! of springs iii to a frame member (not shown) of the sequence switch. For a more detailed description of the sequence switch and its manner of operation, reterence may be had to the above mentioned Reynolds et al. patent.

Referring particularly to Figs. 3, 4 and 5 which are detail sectional views of a contact spring assembly or pile-up H the four pair of springs ii are superimposed and insulated from each other by insulator strips 20. At each end of the spring pile-up I4 is a compression plate 2|, the lower plate 2| being provided by the bottom portion of the U-shaped bracket IS. The springs l3 and insulator strips 20 are clamped between the compression plates 2! by belts or screws 22 which extend through openings 23 formed in the springs and strips, the screws being threaded into the lower plate 2!. To electrically insulate the contact springs l3 from the screws 22, insulator sleeves or bushings 24 are arranged to surround the screws between the inner opposed faces of the compression plates 2|.

In the present embodiment of the invention, the bushings 24 are composed of material, such as semi-hard rubber, with sufficient pliability when in a fresh state that it will cold flow laterally when compressed lonitudinally and then harden with age. The bushings are cut with a length predeterminedly slightly greater than the final distance between the inner opposed faces of the compression plates 2| when the spring assembly is fully compressed. An example of the initial length of the bushing 24 relative to its compressed state is shown in Figs. 4 and 3, re spectively. During the compression of the assembly as the screws 22 are tightened the excess material of the bushings 24 will flow laterally and fill the slight annular clearance space 25 (Fig. 5) between the bushing and the inner periphery of the openings 23 in the springs and insulator strips and upon being fully compressed will appear as illustrated in Fig. 3. Thus since the bushings while being assembled and compressed are pliable and non-frangible, no breakage thereof will occur and any loose metal particles in the form of chips or burrs in the assembly will be retained permanently in position where they will produce no short circuit or will produce a short circuit which will be detected. during inspection.

For economy in manufacture, it is desirable that the rubber used for the bushings contain suflicient vulcanizing agent and be vulcanized to a sufficient extent that the rubber may be formed into a fairly rigid tube from which the bushings may be readily cut by machine. Softer rubber, however, may be used if desired.

From the foregoing description, it will be apparent that the invention provides an improved course, that the-invention is not limited to the tor strips after compression, said members being expansible laterally when longitudinally compressed.

2. In an electrical contact assembly, a plurality, of superimposed contact elements, insulator strips therebetween, means including elements extending through openings in the assembly for retaining it under compression, and semi-hard rubber insulating members surrounding the retaining elements, said members being initially exteriorly spaced from the contact elements and insulator strips and sufiiciently soft to cold flow laterally when compressed longitudinally and of an initial length slightly greater than the final height of the contact elements and insulator strips after compression,

3. In an electrical spring contact assembly, a plurality of superimposed contact springs, insulator strips therebetween, external compression plates, compression retaining elements extending through openings in the assembly, and pliable insulating sleeves surrounding the retaining ele ments between the compression plates, said sleeves being initially exteriorly spaced from the contact springs and insulator strips of a length slightly greater than the final height of the conand semi-hard rubber insulating sleeves surrounding the screws between the compression plates, said sleeves being initially exteriorly spaced from the contact springs-and insulator strips and sumciently soft to cold flow laterally when compressed longltudinally and of an initial length slightly greater than the final height of the contact springs and insulator strips after compression.

AARON G. ANDEEN. 

